Titration TGA is a method for dosing a gas or a vapor aliquot (i.e. of known amount) on a sample being
weighed by a TGA balance. It can be applied to the study of physisorption or chemisorption phenomena
and to some extent to all gas-solid reactions (e.g. oxydo-reductions).

The emissions of volatile organic compounds (VOC) has become one of the main concerns of numbers of industries. Due to their major impact on the environment and human health, international policies have become more and more restrictive with regard to VOC emissions. Moreover, their poor chemical compatibilities with many materials may lead to damages when they are evolved in confined systems.

Mixing calorimetry cells aim at putting in contact two or more substances in the sensitive part of the calorimeter after having stabilized them to the same test temperature. The heat release linked with the interaction between the substances is then measured from the very first moments. Such a setup allows determining thermodynamic and kinetic parameters of processes such as a chemical reaction, an adsorption, or a dissolution.

The input of hyphenated techniques in the field of thermogravimetric analysis has now long been proved, with a large number of applications for TG-MS or TG-FTIR. They have showed themselves particularly interesting when the chemistry of a reaction or thermal decomposition has to be elucidated thanks to the qualification of the evolved chemicals.
However, these techniques are limited in numerous cases, especially when a large number of molecules are evolved in a short period of time, or more specifically in the field of TG-MS if high molecular weight molecules are ionized into multiple smaller fragments. This is particularly the case when analyzing the thermal decomposition of complex organic substances such as biomass or polymeric materials.
This is why the technique of TG-GC-MS is becoming increasingly popular, as gas chromatography allows a first separation of the evolved species, before their identification by the mass spectrometer.

The plate-type DSC technique is today a largely used technique for the thermal investigations of materials up to very high temperature (1600°C). However the main limitation of the technique is the small amount of material that can be investigated. In the case of weak thermal effects or also for experiments on non homogeneous samples, the results provided by the plate-type DSC technique are most of the time very poor. In order to provide a better solution for these types of investigations, Setaram has selected the technology developed around the Calvet principle (3D) sensors that has been successfully used for many years in the development of calorimetric detectors. Based on this expertise, a 3D DSC detector was designed to be used on the Labsys DSC for the Cp determination at high temperature, but also for the investigation of large amounts of samples up to 1600°C.

Modern industry requires more and more materials resisting to high and very high temperatures. A good characterization of these materials is becoming necessary in order to precisely measure their properties, to know their field of applications and also their limits of use. Among all the properties needed, heat capacity data are required at high temperature to be combined with thermal conductivity and thermal diffusivity.For material scientists there is a key issue to accurately measure the heat capacity of samples, especially at high temperatures. Many calorimetric devices and methods have been used to meet the requirements but the DSC technique remains the most often used for such a determination. The major difficulties in this case, besides the matters of simply reaching high temperatures or building measurement systems with materials than can stand high temperatures, is to overcome the drop of sensitivity of commonly employed thermocouples when approaching their upper limit of use or to deal with perturbations linked with the radiation effects of the measured samples. Another difficulty is related to the plate-type DSC technique that limits the amount of material to be investigated.The solution is to use the technology developed around the Calvet principle (3D) sensors that has been successfully used in the accurate determination of specific heat with various types of thermal analyzers. Based on this expertise, a 3D detector was designed to be used on the Labsys DSC for the Cp determination at high temperature.

The Thermal Energy Storage (TES) is defined as the temporary storage of thermal energy at high or low temperatures. As most of the renewable energy sources (solar, wind, …) are intermittently available, the target of TES is to improve performances of energy systems with a smoother supply and an increased reliability.For each TES mode, various types of transformations or reactions are available and are well known. This application note will demonstrate how the thermal analysis and calorimetric methods are used to investigate the
different TES techniques and to characterize the materials (solid and liquid) used in the corresponding processes.

The boiling point of a pure compound is one of the essential information necessary to know before any industrial implementation. Nevertheless, its determination needs very specific conditions to limit the influence of the atmosphere. Indeed, internal gas convection, vapor pressure in the crucible or kinetic of vaporization are important factors that play an important role in the measurement. To determine precisely the boiling point, those factors have to be optimized. The DSC technique can be used for such a measurement

With the recent advances in solid state research and the development of new synthesis paths, only small amounts of material are produced. To investigate the sorption properties of these small samples an accurate tool for measurement is required. The PCTPro-2000 can measure sample quantities down to mg’s thank to its Microdoser attachment

Calibration is essential for a calorimeter : the accurate determination of the calibration factor conditions the quality of the obtained results of energy. In a conventional DSC the heat transfer between the sample and the heat sink passes through the lower part of the crucible. In a Calvet type DSC such as DSC111, DSC121 and microDSC’s, this heat transfer is done in all directions. These properties give to Calvet type DSC much better metrological properties such as the linearity of the output of a DSC to power dissipated in its heart.

To assess the thermal expansion coefficient of a sample, the variation in length of this sample, ?L sample, has to be plotted against temperature T. With a non-differential system, the raw expansion curve obtained can be described by the following equation : ?L sample – ?L assembly + drift = f(T)
?L assembly is due to the expansion of the material making up the probe and the sample-holder tube which is not compensated for the length of the sample. The drift term is due to a temperature gradient between the sample-holder and the probe. With an adapted software it is possible to correct the raw data of the two above interfering terms and thus obtain the expansion curve of the sample.

The thermomechanical behavior of fibers or films can be highlighted by using a special device for traction studies. The sample is maintained between two clamps. The upper clamp is linked to the sample-holder tube whereas the lower clamp exhibits a hole in which the hooklike end of the probe is introduced.

The SetsysTMA allows measuring variations in dimension of the sample when this sample is subjected to a temperature program under a non-oscillatory load. Dilatometric measurements under small loads can be carried out with SetsysTMA as well as stress-strain studies under various deformation modes (compression, penetration, traction, flexure) with appropriate probes.
Depending on the temperature range, three versions are available.

On using the circulation mixing vessel it is possible to inject two different liquids continuously. Thus, the titration of an acid by a base is possible. On changing the flow-rates given by the two pumps the ratio HCI / NaOH is modified, but the total flow-rate is kept constant. For this application the micro-DSC must be used with a pair of circulation mixing vessel (S60/112014), the temperature prestabilizer (S60/26626) and two Peristaltic 2-channel pumps (2 times S60/29332)

Some experiments carried out at constant temperature consists of monitoring the calorimeter output over a long time period and measurements of minor thermal variations. To be sure that the measurement is significant it implies that the calorimetric output with an inert sample must be very stable. The curve shown below is the type of curve that could be expected on using the standard equipment without any special devices like main stabilizers, thermostated water circuit or air conditioners : it has been carried out in a normal room but under the following conditions : no heating system, closed shutter, no air stream in the room : the general rule is to avoid any rapid room temperature variation.

Some experiments require monitoring the thermal behavior of a substance at successively different temperatures (see sheet AN334 : Propellant stability).
Some instruments available on the market have a water bath of 20-30 liters and for this reason are thermally very inert : after a modification of the set temperature they require about 24 hours to have a stable signal. The curve here under shows the calorimeter response after a set temperature modification.

Connected to the Joule effect calibration device (S60/1429) this vessel consists of a resistor, which dissipates a constant heat power. The value of the power can be selected on the calibration device. Linked to a microcomputer the procedure of calibration is the automatic : it provides the calibration curve on the whole temperature range.

The accuracy of the measurement of the heat capacity of the liquid by calorimetric method depends on a correction term due to the vapor phase above the liquid. In order to overcome this difficulty, a special calorimetric vessel has been designed. The main feature is a tube welded to the experimental vessel. It is filled through one tube by means of a syringe, until the liquid comes out through a second tube. When the liquids is heated it expands freely in the tubes but the volume of the liquid in the vessel, located in the detection zone of the calorimeter remains constant. The determination of the heat capacity of this corresponding volume is achieved using the step heating mode.
Notice : the heat capacity can also be measured by using the sealed vessel (S60/1528).
The sample is then in the presence of its vapor pressure : it is suitable for solids but can sometimes also be used for liquids.

With this vessel it is possible simultaneously to introduce two liquids. They are injected by two peristaltic 2-channel pumps (S60/29332) or by gravity.
The liquids enter first the temperature prestabilizer (S60/26626) through which they flow in a loop. In this zone the temperature of the liquid equilibrates to the temperature of the calorimeter. The two inlet liquids are then forced to be mixed through a mixer. The resulting heat is then monitored by the transducer. The mixture exits through the outlet tubing.

With this vessels it is possible to introduce a liquid (or a gas). The liquid enters first the temperature prestabilizer (S60/26626) in which it flows in a loop. In this zone the temperature of the liquid equilibrates to the temperature of the calorimeter. The liquid then enters the lower part of the vessel. The liquid (gas) then exits via the outlet tubing. Generally a peristaltic pump is used (S60/29332).

This liquid and gas tight vessel is used for any kind of investigation which requires the analysis of a liquid or a solid totally sealed off from the outside environment. For example even minute sample loss through evaporation is avoided. The seal is obtained by the elastomer 0-ring.

The DTA rod made of tungsten rhenium can be calibrated by a melting of a standard such as sapphire.
At very high temperatures, only sapphire can be used because properties like melting point and enthalpy are well defined. The temperature given by thermocouples can be checked and the DTA signal calibrated.

The DTA transducer is made of tungsten and tungsten rhenium thermocouples to work up to 2400°C. It is less sensitive than a classical DTA rod made of platinum but small energy changes can be detected. Rhodium is a good example with a small enthalpy of melting of 50 cal/g.

The alumina tube used up to 1750°C is removed to work up to 2400°C. The experiment is run directly in the graphite resistor under vacuum or inert gas (except nitrogen).
The TGA-DTA probe used is made with a tungsten plate and four wires in W/Re for the measurement of the temperature of the sample and the DTA signal up to 2400°C.

Coupling a Fourrier Transformed Infrared Spectrometer makes it possible to identify evolved gas during a thermal analysis. All products of decomposition can be detected and compared with reference spectrums, except for metallic or monoatomic compounds.
This powerful method has application in many fields ; polymers, inorganic materials, fiber..

Thermogravimetry measures the mass loss or gain of the sample and DTA detects the corresponding thermal effects. But, these two methods do not identify the type of reaction or decomposition which measure the mechanism of the transformation. With a mass spectrometer linked to TAG, gases with a molar mass between 1 and 300 g are controlled with a high detection limit.

Mass loss of organic compounds are sometimes very long because they are enclosed in a mineral. For a long term experiment, it is important to have a good regulation of temperature and a controlled atmosphere, without leaks, in order to protect the sample from air exposure.
Analyzed oil-bearing rock contains organic compounds ; evolved compounds should be a function of a temperature level similar to a distillation.

Some compounds have a high vapor pressure or evolved gas which are reactive with platinum or alumina.
These materials can be analyzed in sealed crucibles (fig. 1) under vacuum or known atmosphere. The sensitivity of the DTA transducer is more than enough to detect thermal effects.
Experiments were run with sulfides which are reactive to platinum at low concentrations.

The major advantage of the TGA-DTA rod is analysis on the same sample. Thermogravimetry and thermal analysis can be quantitative thanks to a calibration of this rod.
Melting of metals gives a sensitivity of the rod at different temperatures and quantitative analysis can be run. The enthalpy of a thermal effect can be calculated when introducing the calibration of the rod into the computer during a data treatment.

The TAG provides the investigator with a symmetrical TGA-DTA system which means with two furnaces. Deviation on the thermogravimetric signal is equivalent to 1.5 mg at 1000°C with a monofurnace system. That is only due to the combined resulting form the buoyancy effect which vary with the density of the gas, combined with the driving force produced by flowing gases and other disturbing effects.
These perturbations are physically compensated with a second furnace. Moreover, thanks to homogeneity in the furnaces, the DTA signal is stable.

The Calvet Low Temperature calorimeter BT 2.15 is especially designed for calorimetric investigations from very low temperature (-196°C) up to medium temperature (200°C). The size of its experimental vessels is identical to the C80 one. In order to have compatible vessels on the C80 and the BT 2.15, identical vessel bodies are used for the standard, vacuum and gas circulation vessels (normal and high pressures). The length of the pipe connecting the vessel to the outside is different.

Many organic materials used in chemical reactions exhibit an hazardous behavior when heated. Their composition may produce a large amount of vapor and increase very highly the pressure in the reactor. So the pressure, especially its evolution during the reaction, has to be well known in order to design correctly the reactor and the safety devices to prevent any risk of explosion and destruction of the reactor. Chemical plants are especially interested in this pressure control during reaction or storage.
SETARAM has designed a calorimetric high pressure vessel linked with a pressure gauge in order to evaluate in the same time the pressure evolved during the reaction and to follow the heat dissipated. Both data can be used to calculated the reactor dimensions and to evaluate the risk of decomposition.

In most organic reactions, the stirring of the mixture has to be maintained during the reaction for a good homogeneity of the mixture and for improving the efficiency of the reaction. In industrial reactors, large amounts of chemical products are continuously mixed by means of mechanical stirrers. It can be the reaction of two liquids giving a crystallized solid, or the mixing of a liquid and a solid giving another solid, or also reactions between solids. In all cases, stirring and sometimes strong stirring, is needed.
SETARAM has designed a mixing vessel linked with a mechanical stirrer in order to simulate types of reactions and to evaluate what is the heat evolved during mixing and reaction. These data are helpful to design the reactor and its cooling system.

The accuracy of the heat capacity of a liquid by the calorimetric method depends on the corrective term due to the vapor phase above the liquid. In order to overcome this difficulty, a special calorimetric vessel has been designed. The main feature is a tube welded to the experimental vessel. Its filling is done through the tube by means of a syringe, until there is liquid in the tube. The top of the vessel is machined so that there is no vapor or bubble retained in the experimental vessel. When the liquid is heated the liquid expands freely in the tube, but the volume of liquid in the vessel, located in the direction zone of the calorimeter remains constant. The determination of the heat capacity of this corresponding volume is achieved using the step-heating mode.

Many powdered compounds (catalysts, oxides, coals,..) are characterized by their surfaces. The measurement of physical or chemical interactions between any solute with the surface of powders characterizes their reactivity. Flow calorimetry is well-adapted method for such an investigation. The liquid percolation vessel enables the liquid to pass through the powder, deposited on a poral filter. The typical experimentation consists in using a first percolation of a carrier liquid in order to achieve the wetting of the powder. Then it is substituted by a solute and the adsorption heat of the solute on the powder is directly measured. After this process the solute is replaced by the carrier liquid and the adsorption heat is measured.

For some types of mixing, the reversal mixing vessel (see application sheet TN252) is not adapted : incompatibility of mercury with the samples, mixing of viscous substances. It is replaced by the mixing vessel with membrane. A membrane separates the two chambers eliminating the use of mercury. Mixing is performed by piercing the membrane by a rod which also acts as a stirrer (manual stirring). In the case of viscous substances or formation of a solid during the reaction, a continuous stirring is obtained by adapting a driven motor on the rod. When possible the reversal mixing vessel is preferred to the mixing vessel with membrane. It gives a better precision (no connection with outside).

The two chambers of the reversal mixing vessel are separated by a tilting lid. The samples (liquid-liquid or liquid-solid) are separately introduced into the vessel outside of the calorimeter. In order to obtain a complete separation of the chambers, a mercury seal on the lid can be used. If the vapor pressures of the samples are low, the mercury seal is not required. After the introduction of the vessels into the calorimeter, the thermal equilibrium is to be achieved in order to have the two separated components at the same temperature. Then, mixing is performed by reversing the calorimeter. If the samples mix easily, only a few rotations of the calorimeter are necessary. In the case of difficult mixing, the reversing mechanism can be maintained during the whole test.

In the gas circulation vessels, the connection consists of two coaxial pipes, to enable the continuous and intermittent circulation of gas on the sample (liquid or solid). At the outlet of the vessel, the evolved gases carried by the sweeping gas can be analyzed on line through a gas analyzer. The gas circulation vessels are used with different types of carrier gas (inert, reductive, oxidative) at various pressures, depending on the model of vessel. Using an adapted gas circuit, different ways of experimentation are possible : use a simple carrier gas, or start an experiment with inert gas and switch for active gas in the second part of the experiment, or introduce an active gas in the carrier gas.

The main feature of the vacuum vessels is the connection pipe between the container and outside. Vacuum in the container and also a static pressure of gas are obtained through the pipe. With this facility, different types of experiments are possible : purge the sample before applying a pressure of inert gas, work under vacuum or reduced pressure, work under static pressure of reactive gas (up to 100 bars).

The standard vessels are simple tight containers to be used in the C80 calorimeter when the experiment requires no physical contact between outside and sample. Depending on the internal pressure in the container (gas evolved during heating) two models are available : the normal pressure vessel for investigations at medium temperature (220°C) and low pressure (5 bars) and the high pressure vessel for investigations at higher temperature (300°C) and high pressure (100 bars).

Isothermal thermogravimetry is a very interesting method for the investigation of gas adsorption. An experimental thermogravimetric device is described, which allows running such tests at low temperature under reduced pressure, or with a linear programmation of the pressure. This is particularly well adapted for the determination of specific surface of compounds, and also to measure the capacity of gas adsorption of molecular sieves at low temperature.

Many solid porous compounds, especially zeolites, are well known for their adsorbing properties. In order to measure their adsorption capacity, a special experimental set-up has been designed for the C80 calorimeter. This device allows characterizing the adsorption of vapor on a solid under reduced pressures. The liquid to be adsorbed is initially frozen, then kept at a well-defined temperature, determining a well-known vapor pressure. This vapor is adsorbed on the solid, previously regenerated under vacuum.

Gas adsorption investigation requires a good contact between the gas and the solid. A silica reactor has been designed for the Calvet DSC111 in which the reactive gas flows through the sample situated on a sintered glass. This particular cell design is especially interesting for the gas-solid reactions or also for the investigation of reactions occurring in a corrosive medium. The exhausted gases are easily analyzed at the outlet of the silica tube by means of a gas chromatograph or a mass spectrometer (see application note AN226).

Applications of many powdered compounds (catalysts, oxydes, coals..) are dependent on their surfaces. The measurement of physical or chemical interactions between any solute with the surface of powders characterizes their reactivity.
Flow calorimetry is a well adapted method for such investigation. A special flow cell is designed and allows the percolation of liquids through a powder. The solutes are introduced in a carrier liquid. Adsorption and desorption reactions can be investigated.

For special applications (oxidation, reduction, decomposition), the pressure of reactive gas must be initially fixed in the experimental crucible. The described pressurization device is designed for the initial pressurization of the sealed high pressure crucibles with inert or reactive gases, after a previous degassing of the sample. The stainless steel crucibles are sealed under the pressure chosen on the control high pressure panel.

The batch mixing cell enables two liquid bodies (or one liquid body and one powder body) to be mixed and their mixing heat to be measured. The mixing cell comprises two volumes that are initially hermetically separated by a membrane. As is shown in Figure 1, a piston fitted with a mixer is used to pierce the membrane. In a second phase, two sample volumes are brought into full mutual contact and mixed in a continuous and equal manner in the measuring and reference cells

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